Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Reciprocal rate constant

The rate constants k and ki may be related to the concepts of the preceding section as follows. First, k is simply the reciprocal of the adsorption time, that is. [Pg.605]

Not surprisingly, we find that the relaxation is a first-order process with rate constant A , + A i. It is conventional in relaxation kinetics to speak of the relaxation time T, which is the time required for the concentration to decay to Me its initial value. In Chapter 2 we found that the lifetime defined in this way is the reciprocal of a first-order rate constant. In the present instance, therefore,... [Pg.138]

We have next to consider the measurement of the relaxation times. Each t is the reciprocal of an apparent first-order rate constant, so the problem is identical with problems considered in Chapters 2 and 3. If the system possesses a single relaxation time, a semilogarithmic first-order plot suffices to estimate t. The analytical response is often solution absorbance, or an electrical signal proportional to absorbance or to another physical property. As shown in Section 2.3 (Treatment of Instrument Response Data), the appropriate plotting function is In (A, - Aa=), where A, is the... [Pg.142]

Metwally et al. [28] also studied the resin-catalyzed hydrolysis of ethyl formate in acetone-water mixtures at different temperatures. The experimental results indicated a linear dependence of the logarithm of rate constant on the reciprocal of the dielectric constant (Fig. 2). The decrease of dielectric constant may lower the concentration of the highly polar transition state and thereby decrease the rate [28]. [Pg.779]

This is the general expression for film growth under an electric field. The same basic relationship can be derived if the forward and reverse rate constants, k, are regarded as different, and the forward and reverse activation energies, AG are correspondingly different these parameters are equilibrium parameters, and are both incorporated into the constant A. The parameters A and B are constants for a particular oxide A has units of current density (Am" ) and B has units of reciprocal electric field (mV ). Equation 1.114 has two limiting approximations. [Pg.130]

Notice that for a first-order reaction the rate constant has the units of reciprocal time, for example, min-1. This suggests a simple physical interpretation of k (at least where k is small) it is the fraction of reactant decomposing in unit time. For a first-order reaction in which... [Pg.294]

Equilibrium (dissociation) constant, reciprocal of the association constant and affinity characterizes the binding of a molecule to a receptor. Specifically, it is the ratio of the rate of offset of the molecule away from the receptor divided by the rate of onset toward the receptor. It also is a molar concentration that binds to 50% of the receptor population. [Pg.278]

In Fig. 28, the abscissa kt is the product of the reaction rate constant and the reactor residence time, which is proportional to the reciprocal of the space velocity. The parameter k co is the product of the CO inhibition parameter and inlet concentration. Since k is approximately 5 at 600°F these three curves represent c = 1, 2, and 4%. The conversion for a first-order kinetics is independent of the inlet concentration, but the conversion for the kinetics of Eq. (48) is highly dependent on inlet concentration. As the space velocity increases, kt decreases in a reciprocal manner and the conversion for a first-order reaction gradually declines. For the kinetics of Eq. (48), the conversion is 100% at low space velocities, and does not vary as the space velocity is increased until a threshold is reached with precipitous conversion decline. The conversion for the same kinetics in a stirred tank reactor is shown in Fig. 29. For the kinetics of Eq. (48), multiple solutions may be encountered when the inlet concentration is sufficiently high. Given two reactors of the same volume, and given the same kinetics and inlet concentrations, the conversions are compared in Fig. 30. The piston flow reactor has an advantage over the stirred tank... [Pg.119]

The half-time (or half-life) of the reaction is independent of [A]o. The reciprocal of the rate constant, t = l/k, is referred to as the lifetime or the mean reaction time. In that time [A] falls to l/e of its initial value. The pharmaceutical industry refers to the shelf life or t90, the time at which [A]/[A]o reaches 0.90. Both t and t90 are also independent of [A]o. [Pg.16]

If the equilibrium is suddenly displaced, the results obtained in Chapter 3 show that the re-equilibration process will follow first-order kinetics. It is customary in this field to refer to r, the relaxation time, which is defined as reciprocal of the first-order rate constant for re-equilibration. In this case, we have... [Pg.258]

This was proved by showing that the reciprocal of the life-time of the pivaloyl ion, t5co+> is independent of the concentration of t-butyl ion. A mechanism based on equation (7) would have resulted in t5,co+ being proportional to [t-C4H ]. The rate constant of decarbonylation of t-C4H9CO+ in HF—SbFg (equimolar) and in FHSO3—SbFs (equimolar) was determined to be sec. This... [Pg.32]

HO-oxidation of an individual NMHCj produces H02 radicals with a yield aj, and oxidation of the NMHC oxidation product produces H02 in stoichiometric amount The lumped coefficients or yields a and p need not be integers, and represent the effectiveness of a particular NMHCj in producing RO2. and H02 radicals (lumped together as HO2) that will then oxidize NO. to N02 in processes such as R6 and R13, producing one net ozone molecule each. Alternatively, when the NO. concentration is low, peroxyl radicals may form PAN (as in R22) or hydrogen peroxide (as in R33) which are other oxidant species. In this formulation, transport is expressed by an overall dilution rate of the polluted air mass into unpolluted air with a rate constant (units = reciprocal time dilution lifetime=1// ). This rate constant includes scavenging processes such as precipitation removal as well as mixing with clean air. [Pg.75]

Since S/t has units of moles per volume per time and a has units of moles per volume, the rate constant for a first-order reaction has units of reciprocal time e.g., s. The best example of a truly first-order reaction is radioactive decay for example,... [Pg.6]

Observe that aok has units of reciprocal time so that aokt is dimensionless. The grouping OQkt is the dimensionless rate constant for a second-order reaction, just as kt is the dimensionless rate constant for a first-order reaction. Equivalently, they can be considered as dimensionless reaction times. For reaction rates governed by Equation (1.20),... [Pg.13]

The units on [CH3CeH4S02H] are inverse molarity. Reciprocal concentrations are often cited in the chemical kinetics literature for second-order reactions. Confirm that second-order kinetics provide a good fit and determine the rate constant. [Pg.251]

The primary characteristic of a sequential blocker, as observed with the patch clamp technique, is that the reciprocal of the mean duration of the lifetime equals the normal channel closing rate plus the rate constant of channel blockade times the drug concentration. Therefore, increasing the drug concentration shortens the mean channel open time. [Pg.114]

The decomposition data forjNO plotted as the reciprocal of concentration vs. time. This graph is linear, with a slope equal to the second-order rate constant. [Pg.1072]

We can determine the activation energy from a series of measurements by plotting the logarithm of the rate constant against the reciprocal temperature, as rearrangement of Eq. (45) sho vs ... [Pg.37]

Thus, a plot of In k versus the reciprocal temperature should yield a straight line with slope -E/Rg and In ko. These two kinetic parameters are strongly interconnected even a minor change in slope evaluation will result in a major change of the intercept. Theoretically, values of rate constants at two temperatures are sufficient to estimate the activation energy ... [Pg.316]

This equation has two parameters t, the mean residence time (z = V/F) with dimensions of time and k, the reaction rate constant with dimensions of reciprocal time, applying for a first-order reaction. The concentration of reactant A in the reactor cannot, under normal circumstances, exceed the inlet feed value, Cao and thus a new dimensionless concentration, Cai, can be defined as... [Pg.48]

FIG. 29 Oxygen-transfer rate constants derived from Fig. 28 as a function of the reciprocal of the interfacial area per molecule. (Reprinted from Ref 19. Copyright 1998 American Chemical Society.)... [Pg.327]

Here X denotes lb-moles of benzene per lb-mole of pure benzene feed and x, denotes lb-moles of diphenyl per lb-mole of pure benzene feed. The parameters k, and k2 are unknown reaction rate constants whereas K, and K2 are known equilibrium constants. The data consist of measurements of Xi and x2 in a flow reactor at eight values of the reciprocal space velocity t. The feed to the reactor was pure benzene. The experimental data are given in Table 6.2 (in Chapter 6). The governing ODEs can also be written as ... [Pg.130]

When [El] has been reduced to the point that it is equal in concentration to [EI Je, the natural logarithm of the ratio /f/, /[ 7]0 would be ln(l/< ) = -1.0. The length of time required for [EI to decay by this amount can be obtained from the semilog plot shown in Figure A1.4B. This time interval is referred to as the relaxation time or the time constant and is given the symbol x. The relaxation time is the reciprocal of the rate constant ... [Pg.254]

Note that since the relaxtion time x has units of time, the rate constant must have units of reciprocal time. Thus the rate constant for a first-order reaction give a measure of the frequency, or periodicity, of reaction (i.e., events per unit time). [Pg.254]

The additional concentration term in Equation (A1.23), compared to Equation (A1.8), requires that the rate constant here, koa, have units of reciprocal time, reciprocal molarity (most commonly M 1 s ) in order for the velocity to be expressed in units of molarity per unit time. Equation (A1.23) can be recast in terms of the initial reactant concentrations ... [Pg.256]

Note that because kon is a second-order rate constant, and koff is a first-order rate constant, the units of Ka will be reciprocal molarity and the units of Kd will be molarity. [Pg.258]

From Eq. (6.2), the mean open time is predicted to be the reciprocal of the rate constant for channel closing (xopen = 1/a). For bursts recorded at very low agonist concentrations, the mean closed time within bursts, xg, is equal to 1/( 3 + 2k 2), and the mean number of gaps per burst, N, is equal to 3/2 2. Using these two simultaneous equations, it is then possible to calculate (3 and k 2. [Pg.192]

The reciprocals of the time constants, x, and x2, are the rate constants k, and k2. The weights of the exponentials (ii and w2) are complicated functions of the transition rates in Eq. (6.25). Flowever, the rate constants are eigenvalues found by solving the system of differential equations that describe the above mechanism. A, and k2 are the two solutions of the quadratic equation ... [Pg.198]

The reciprocal of the rate constant (l/k) for a particular process is called the eth life. This corresponds to the time necessary for the population of a state to decay to l/e times the original population via that particular process. [Pg.11]

Since (/iv//av)/(/i//2) can be measured and kx and k2 are just the observed reciprocal decay constants of levels tx and r2, it is possible to determine the ratio of the intersystem crossing rate constants K KX. This information is difficult if not impossible to obtain in other ways. The results for several molecules are shown in Figure 6.3. [Pg.444]


See other pages where Reciprocal rate constant is mentioned: [Pg.60]    [Pg.60]    [Pg.1132]    [Pg.2815]    [Pg.136]    [Pg.272]    [Pg.272]    [Pg.67]    [Pg.26]    [Pg.45]    [Pg.608]    [Pg.338]    [Pg.405]    [Pg.162]    [Pg.183]    [Pg.200]    [Pg.99]    [Pg.304]    [Pg.310]    [Pg.80]    [Pg.140]    [Pg.404]   
See also in sourсe #XX -- [ Pg.260 ]




SEARCH



© 2024 chempedia.info